Hello Everyone, noob here and was looking for some help with some LED lights! I'm hoping for a design but maybe this question is not allowed. I am not building an array and understand some of the concerns posted on this subject of automotive issues. Actually I do not think this applies to the issue I have at hand.
So here goes, I have stock third brake lights from an automobile, I want to add them to my motorcycle as ADDED, ADDITIONAL, lighting to the rear of this bike. These units are rated at 12vdc and are nice and brite of the proper color. Adding a resistor of 180ohms dims to a perfect tail/running light. Which would be energized when key/on. I want to also energize this same LED from the brake switch and turn signal. That's the trick! diodes to block the second or third input to the single input LED.
I'm asking for some help with this circuit, I was an ET in the Navy but that was many,many moons ago,lol 1974-1977 USS Guam LPH-9. Haven't worked much with electronics since I hired into a toolmaker apprenticeship in 1981. Still have some knowledge left but DIMM,lol I do know you cannot feed 12vdc on three wires to one without blowing some fuses.
I'm thinking I need some paralell resistance to the diodes, or maybe zener diodes. I know this is a simple problem for someone and if I was still working at GM I could get the problem solved. Been retired for a few years now and have lost touch with my electronic guru buddies that helped me with other projects in the past.
Well, thanks for taking the time to read this and maybe it's not a banded subject matter and I can get some help lighting up the back of my motorcycle. Judge

So you want to dim the light with a 180 Ohm resistor for an always on daytime running light. Then when you brake or use the turn signal you want to, I assume, brighten it by excluding the 180 Ohm series resistance.

I'm still working on the problem, but yes, 180ohm is perfect for running light. Full brightness for brake input or the turn input. Didn't really want to wire in a relay but will consider. Hope to wire inline, similar to the 2 to 3 type set-up but this would be a 2 to 4 wire, ground,running,stop,turn.
Thanks for any info. Judge

I did some checking and rewire. I have all three inputs with no fuse or circuit breaker problems. Running light to brake or turn works fine, here's the problem now! the engerized brake input overrides the turn signal input. NO turn signal when brake light engerized. Which leads me to beleive that as mentioned I need some sort of relay switching off the brake voltage when a turn signal is engerized.
Does this seem correct? Would need one for each side? Thanks Judge
PS I am calc. the running voltage at 13.5vdc. The resistor drops 4.45vdc and the resistor and diode together 5.24vdc that is measured with circuit engerized, but did not measure that voltage, it's from a 12vdc charger. Hope that helps The charger was low voltage! hooked up power supply set at 13.5 res. 5.7vdc 6.56vdc diode and resistor.

Well, been doing some reading and experimenting. Got the thing working except the brake stays on for 20sec after no signal, I thought it was due to zener diode voltage. then a wire came apart ad it works as a three wire system from the control module in this case. I hade no idea, and the directions for the thing did not mention anything except brake, running, and turn signal wires. Who Knew that it was actually a turn/stop wire,duh
I'm thinking I still have some testing and measuring to do but hope all's well. Thanks for helping get my mind going again! Been a long time since I dove into some electronics, simple electronics at that. Again thanks for the insight and I'll send back some drawings when I get them done. Judge